An apparatus of this type is known from WO 2008/025 555 A1. With this known apparatus, it is possible, with high stock removal rate and large removal surface, to mine rock or other hard materials economically, wherein the mill cutting or stock removal takes place radially outside the periphery of the tool drum. The known apparatus can advantageously be used to drive galleries or tunnels with the aid of part-face heading machines provided with an arm which is pivotable transversely to the main direction of advance and on the front end of which the tool drum is rotatably mounted. Such an apparatus can also be used, however, on mining machines for longwall-type extraction at the face.
In the known apparatus, it is also known to arrange the shaft axes of the tool carriers inclined by a few degrees in relation to the radial direction of the drum axis, whereby, when the apparatus is advanced in the axial direction of the tool drum, a good loosening result is achieved. It has been shown, however, that when the known apparatus is used on a machine extension arm which is pivoted from one side to the other and back, or else is moved back and forth by means of a mining machine at the face, no uniformly good mining result in both pivoting or motional directions is achieved, but rather the milling performance in one pivoting or motional direction of the machine extension arm or of the mining machine is better than in the opposite direction.